Optical imaging system

ABSTRACT

An optical imaging system includes a first lens having a convex image-side surface, a second lens having a convex object-side surface, a third lens having a concave image-side surface, a fourth lens having a concave object-side surface, a fifth lens having a concave image-side surface, a sixth lens having a concave object-side surface, and a seventh lens having refractive power. The first to seventh lenses are sequentially disposed to be spaced apart from each other by an interval in a direction from an object side toward an imaging plane.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/585,210 filed on May 3, 2017, which claims the benefit under 35U.S.C. § 119(a) of Korean Patent Application No. 10-2016-0159269 filedon Nov. 28, 2016 in the Korean Intellectual Property Office, the entiredisclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND 1. Field

The following description relates to a telescopic optical imaging systemincluding seven lenses.

2. Description of Related Art

Telescopic optical imaging systems capable of capturing images ofdistant objects may be significantly large. In detail, in terms oftelescopic optical imaging systems, the ratio (TL/f) of the overalllength TL of a telescopic optical imaging system to the overall focallength f may be higher than or equal to 1. Thus, it may be difficult tomount telescopic optical imaging systems in small electronic devices,such as portable terminals.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an optical imaging system includes a first lenshaving a convex image-side surface, a second lens having a convexobject-side surface, a third lens having a concave image-side surface, afourth lens having a concave object-side surface, a fifth lens having aconcave image-side surface, a sixth lens having a concave object-sidesurface, and a seventh lens.

The first lens of the optical imaging system may have a convexobject-side surface along the optical axis. The second lens of theoptical imaging system can have a concave image-side surface along theoptical axis. The third lens of the optical imaging may have a convexobject-side surface along the optical axis. The fourth lens of theoptical imaging system can have a convex image-side surface along theoptical axis.

The fifth lens of the optical imaging system may have a convexobject-side surface along the optical axis. The sixth lens of theoptical imaging system can have a concave image-side surface along theoptical axis. The seventh lens of the optical imaging system may haveopposing convex surfaces along the optical axis. The one or both lensesbetween the sixth lens and the seventh lens of the optical imagingsystem can have an inflection point.

In another general aspect, an optical imaging system includes a firstlens having a positive refractive power; a second lens having a negativerefractive power; a third lens having a negative refractive power; afourth lens having a negative refractive power; a fifth lens; a sixthlens; and a seventh lens, sequentially disposed from an object side toan imaging plane. The optical imaging system satisfies the expressionNd2<1.67, where Nd2 represents a refractive index of the second lens.

The optical imaging system may satisfy the expression 0.7<TL/f<1.0,where TL represents a distance from an object-side surface of the firstlens to an imaging plane, and f represents an overall focal length ofthe optical imaging system. The optical imaging system can satisfy theexpression 0.1<f/(Img HT)<2.5, where f represents the overall focallength of the optical imaging system, and IMG HT represents a halfdiagonal length of the imaging plane. The optical imaging system maysatisfy the expression 1.5<Nd5<1.7, where Nd5 represents a refractiveindex of the fifth lens.

The optical imaging system may also satisfy the expression 1.6<Nd7,where Nd7 represents a refractive index of the seventh lens. The opticalimaging system can further satisfy the expression −70<f5/f<70, where frepresents the overall focal length of the optical imaging system, andf5 represents a focal length of the fifth lens. The optical imagingsystem may satisfy the expression 2.4<f/EPD<2.8, where f represents theoverall focal length of the optical imaging system, and EPD represents adiameter of an entrance pupil.

In another general aspect, an optical imaging system includes a firstlens, a second lens, a third lens, a fourth lens, a fifth lens, a sixthlens, and a seventh lens, sequentially disposed from an object side toan imaging plane. The first lens has a positive refractive power. Theseventh lens has a convex object-side surface along an optical axis anda convex image-side surface along the optical axis.

The each of the first to seventh lenses of the optical imaging systemmay have an aspheric surface. The first lens of the optical imagingsystem may have a convex object-side surface having a most convex pointof the optical imaging system. The second lens of the optical imagingsystem may have a concave image-side surface having a most concave pointof the optical imaging system. The second lens, the third lens, thefourth and the sixth lens of the optical imaging system each may have anegative refractive power.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an optical imaging system according to a firstexample.

FIG. 2 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 1.

FIG. 3 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 1.

FIG. 4 is a diagram of an optical imaging system according to a secondexample.

FIG. 5 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 4.

FIG. 6 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 4.

FIG. 7 is a diagram of an optical imaging system according to a thirdexample.

FIG. 8 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 7.

FIG. 9 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 7.

FIG. 10 is a diagram of an optical imaging system according to a fourthexample.

FIG. 11 is a set of graphs illustrating aberration curves of the opticalimaging system illustrated in FIG. 10.

FIG. 12 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 10.

FIG. 13 is a rear view of a portable terminal including an opticalimaging system mounted therein, according to an example.

FIG. 14 is a cross-sectional view of the portable terminal illustratedin FIG. 13.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements where applicable. The drawings maynot be to scale, and the relative size, proportions, and depiction ofelements in the drawings may be exaggerated for clarity, illustration,or convenience.

DETAILED DESCRIPTION

Hereinafter, examples will be described as follows with reference to theattached drawings. Examples provide an optical imaging system capable ofcapturing images of distant objects while being mounted in a smallterminal. The disclosure may, however, be exemplified in many differentforms and should not be construed as being limited to the specificembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the disclosure after an understanding of thisapplication.

Throughout the specification, it will be understood that when anelement, such as a layer, region or wafer (substrate), is referred to asbeing “on,” “connected to,” or “coupled to” another element, it can bedirectly “on,” “connected to,” or “coupled to” the other element orother elements intervening therebetween may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to,” or “directly coupled to” another element, there may be noelements or layers intervening therebetween. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Although terms such as “first,” “second,” and “third” may be used hereinto describe various components, regions, or sections, these components,regions, or sections are not to be limited by these terms. Rather, theseterms are only used to distinguish one component, region, or sectionfrom another component, region, or section. Thus, a first component,region, or section referred to in examples described herein may also bereferred to as a second component, region, or section without departingfrom the teachings of the examples.

The articles “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. The terms“comprises,” “includes,” and “has” specify the presence of statedfeatures, numbers, operations, members, elements, and/or combinationsthereof, but do not preclude the presence or addition of one or moreother features, numbers, operations, members, elements, and/orcombinations thereof.

Due to manufacturing techniques and/or tolerances, variations of theshapes shown in the drawings may occur. Thus, the examples describedherein are not limited to the specific shapes shown in the drawings, butinclude changes in shape that occur during manufacturing.

The features of the examples described herein may be combined in variousways as will be apparent after an understanding of the disclosure ofthis application. Further, although the examples described herein have avariety of configurations, other configurations are possible as will beapparent after an understanding of the disclosure of this application.

According to an example, a first lens refers to a lens closest to anobject or a subject of which an image is captured. A seventh lens refersto a lens closest to an imaging plane or an image sensor. In the presentspecification, an entirety of a radius of curvature, a thickness, adistance from an object-side surface of a first lens to an imaging plane(TL), a half diagonal length of the imaging plane (IMG HT), and a focallength of a lens are indicated in millimeters (mm). A person skilled inthe relevant art will appreciate that other units of measurement may beused. Further, in embodiments, all radii of curvature, thicknesses, OALs(optical axis distances from the first surface of the first lens to theimage sensor), a distance on the optical axis between the stop and theimage sensor (SLs), image heights (IMGHs) (image heights), and backfocus lengths (BFLs) of the lenses, an overall focal length of anoptical system, and a focal length of each lens are indicated inmillimeters (mm). Further, thicknesses of lenses, gaps between thelenses, OALs, TLs, SLs are distances measured based on an optical axisof the lenses.

In a description of a form of a lens, a surface of a lens being convexmeans that an optical axis portion of a corresponding surface is convex,while a surface of a lens being concave means that an optical axisportion of a corresponding surface is concave. Therefore, in aconfiguration in which a surface of a lens is described as being convex,an edge portion of the lens may be concave. In a manner the same as thecase described above, even in a configuration in which a surface of alens is described as being concave, an edge portion of the lens may beconvex. In other words, a paraxial region of a lens may be convex, whilethe remaining portion of the lens outside the paraxial region is eitherconvex, concave, or flat. Further, a paraxial region of a lens may beconcave, while the remaining portion of the lens outside the paraxialregion is either convex, concave, or flat. In addition, in anembodiment, thicknesses and radii of curvatures of lenses are measuredin relation to optical axes of the corresponding lenses.

In accordance with illustrative examples, the embodiments described ofthe optical system include seven lenses with a refractive power.However, the number of lenses in the optical system may vary, forexample, between two to seven lenses, while achieving the variousresults and benefits described below. Also, although each lens isdescribed with a particular refractive power, a different refractivepower for at least one of the lenses may be used to achieve the intendedresult.

An optical imaging system includes seven lenses. For example, theoptical imaging system may include the first lens, a second lens, athird lens, a fourth lens, a fifth lens, a sixth lens, and the seventhlens, sequentially disposed from an object side to an imaging plane.

The first lens has a refractive power. For example, the first lens has apositive refractive power. The first lens has a convex surface. In anembodiment, the first lens has a convex image-side surface.

The first lens has an aspherical surface. For example, both surfaces ofthe first lens are aspherical. The first lens is formed using a materialhaving a relatively high degree of light transmittance and excellentworkability. In an example, the first lens is formed using a plasticmaterial. However, a material of the first lens is not limited to beinga plastic material. In another example, the first lens may be formedusing a glass material. The first lens has a relatively low refractiveindex. In an embodiment, a refractive index of the first lens is lowerthan 1.6.

The second lens has a refractive power. For example, the second lens hasa negative refractive power. The second lens has a convex surface. In anembodiment, the second lens has a convex object-side surface.

The second lens has an aspherical surface. For example, the second lenshas an aspherical object-side surface. The second lens is formed using amaterial having a relatively high degree of light transmittance andexcellent workability. In an example, the second lens is formed using aplastic material. However, a material of the second lens is not limitedto being plastic. In another example, the second lens may be formedusing a glass material. The second lens has a refractive index. In anembodiment, a refractive index of the second lens is lower than 1.67.

The third lens has a refractive power. For example, the third lens has anegative refractive power. The third lens has a concave surface. In anembodiment, the third lens has a concave image-side surface.

The third lens has an aspherical surface. For example, the third lenshas an aspherical image-side surface. The third lens is formed using amaterial having a relatively high degree of light transmittance andexcellent workability. In an example, the third lens is formed using aplastic material. However, a material of the third lens is not limitedto being plastic. In another example, the third lens may be formed usinga glass material. The third lens has a refractive index substantiallysimilar to that of the first lens. In more detail for an embodiment, therefractive index of the third lens is lower than 1.6.

The fourth lens has a refractive power. For example, the fourth lens hasa negative refractive power. The fourth lens has a concave surface. Inan embodiment, the fourth lens has a concave object-side surface.

The fourth lens has an aspherical surface. For example, both surfaces ofthe fourth lens are aspherical. The fourth lens is formed using amaterial having a relatively high degree of light transmittance andexcellent workability. In an example, the fourth lens is formed using aplastic material. However, a material of the fourth lens is not limitedto being plastic. In another example, the fourth lens may be formedusing a glass material. The fourth lens has a refractive index higherthan that of the first lens. In an embodiment, the refractive index ofthe fourth lens is higher than or equal to 1.6.

The fifth lens has a refractive power. For example, the fifth lens has apositive or a negative refractive power. The fifth lens has a meniscusform. In embodiments, the fifth lens may have a meniscus form in whichan object-side surface or an image-side surface is concave.

The fifth lens has an aspherical surface. For example, both surfaces ofthe fifth lens are aspherical. The fifth lens is formed using a materialhaving a relatively high degree of light transmittance and excellentworkability. In an example, the fifth lens is formed using a plasticmaterial. However, a material of the fifth lens is not limited to beingplastic. In another example, the fifth lens may be formed using a glassmaterial. The fifth lens has a refractive index. In an embodiment, arefractive index of the fifth lens is above 1.5 and below 1.7.

The sixth lens has a refractive power. For example, the sixth lens has anegative refractive power. The sixth lens may have a concave surface. Inone example, the sixth lens has a concave object-side surface. The sixthlens may have an inflection point. In embodiments, the sixth lens mayinclude one or more inflection points formed on opposing surfaces.

The sixth lens has an aspherical surface. For example, both surfaces ofthe sixth lens are aspherical. The sixth lens is formed using a materialhaving a relatively high degree of light transmittance and excellentworkability. In an example, the sixth lens is formed using a plasticmaterial. However, a material of the sixth lens is not limited to beingplastic. In another example, the sixth lens may be formed using a glassmaterial. The sixth lens has a refractive index substantially similar tothat of the first lens. In an embodiment, the refractive index of thesixth lens is lower than 1.6.

The seventh lens has a refractive power. For example, the seventh lenshas a positive or a negative refractive power. The seventh lens may haveat least one convex surface. For example, the seventh lens has opposingconvex surfaces. The seventh lens may have an inflection point. Inembodiments, the seventh lens includes one or more inflection pointsformed on opposing surfaces.

The seventh lens may have an aspherical surface. For example, bothsurfaces of the seventh lens are aspherical. The seventh lens is formedusing a material having a relatively high degree of light transmittanceand excellent workability. In an example, the seventh lens is formedusing a plastic material. However, a material of the seventh lens is notlimited to being plastic. In another example, the seventh lens may beformed using a glass material. The seventh lens has a refractive indexlower than that of the first lens. In an embodiment, the refractiveindex of the seventh lens may be lower than 1.53.

Aspherical surfaces of the first to seventh lenses may be expressedusing Formula 1.

$\begin{matrix}{Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {( {1 + k} )c^{2}r^{2}}}} + {Ar}^{4} + {Br}^{6} + {Cr}^{8} + {Dr}^{10} + {Er}^{12} + {Fr}^{14} + {Gr}^{16} + {Hr}^{18} + {Jr}^{20}}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack\end{matrix}$

In Formula 1, c represents an inverse of a radius of curvature of alens, k represents a conic constant, r represents a distance from acertain point on an aspherical surface of the lens to an optical axis, Ato J represent aspherical constants, and Z (or SAG) represents adistance between the certain point on the aspherical surface of the lensat the distance r and a tangential plane meeting the apex of theaspherical surface of the lens.

The optical imaging system further includes a filter, an image sensor,and a stop. The filter is disposed between the seventh lens and theimage sensor. The filter blocks a portion of wavelengths of light, inorder to generate a clear image. For example, the filter blocks light ofan infrared wavelength.

The image sensor forms an imaging plane. For example, a surface of theimage sensor forms the imaging plane. The stop is disposed to adjust anamount of light incident on a lens. In an embodiment, the stop isinterposed between the third lens and the fourth lens.

The optical imaging system satisfies the following ConditionalEquations:

0.7<TL/f<1.0  [Conditional Equation 1]

0.1<f/(IMG HT)<2.5  [Conditional Equation 2]

Nd2<1.67  [Conditional Equation3]

1.5<Nd5<1.7  [Conditional Equation4]

1.6<Nd7  [Conditional Equation5]

-70<f5/f<70  [Conditional Equation6]

2.4<f/EPD<2.8  [Conditional Equation7]

In the Conditional Equations, TL represents a distance from theobject-side surface of the first lens to an imaging plane, f representsan overall focal length of the optical imaging system, and IMG HTrepresents a half diagonal length of the imaging plane. Nd2 represents arefractive index of the second lens, Nd5 represents a refractive indexof the fifth lens, Nd7 represents a refractive index of the seventhlens, f5 represents a focal length of the fifth lens, and EPD representsa diameter of an entrance pupil.

Conditional Equation 1 is provided for the miniaturization of theoptical imaging system. In further detail, in cases in which the opticalimaging system is beyond an upper limit value of Conditional Equation 1,it may be difficult to miniaturize the optical imaging system, so thatit likewise may be difficult to mount the optical imaging system in aportable terminal. In cases in which the optical imaging system is belowa lower limit value of Conditional Equation 1, it may be difficult tomanufacture the optical imaging system.

Conditional Equation 2 is provided for mounting the optical imagingsystem in a portable terminal. In further detail, in cases in which theoptical imaging system is beyond an upper limit value of ConditionalEquation 2, it may be difficult to maintain resolution and telescopiccharacteristics, as well as a relatively wide angle of view. ConditionalEquation 3 is provided for selection of a material of the second lens.

Conditional Equation 4 is provided for selection of a material of thefifth lens. In detail, in cases in which the fifth lens is below a lowerlimit value of Conditional Equation 4, it may be difficult to correctchromatic aberrations. In cases in which the fifth lens is beyond anupper limit value of Conditional Equation 4, it may be difficult tocorrect aberrations by adjusting a distance between the fifth lens andthe sixth lens.

Conditional Equation 5 is provided for selection of a material of theseventh lens. In detail, since the seventh lens satisfying a numericalrange of Conditional Equation 5 has a relatively low Abbe number lessthan or equal to 26, ease of correction of astigmatism, longitudinalchromatic aberrations, and chromatic aberrations of magnification isfacilitated.

Conditional Equation 6 is provided as a design parameter of the fifthlens for a high-resolution optical imaging system. In detail, in casesin which the fifth lens is outside of a numerical range of ConditionalEquation 6, the fifth lens may increase aberrations, so that it may bedifficult to provide a high-resolution optical system. ConditionalEquation 7 is provided as a numerical range of an F number for ahigh-resolution telescopic optical imaging system.

In the optical imaging system, a lens having a relatively high degree ofpositive refractive power may be disposed to be adjacent to an object.In detail, the first lens in the optical imaging system may have thehighest degree of positive refractive power. In the optical imagingsystem, a lens having a relatively high degree of negative refractivepower may be disposed to be substantially adjacent to the imaging plane.In detail, the sixth lens may have the highest degree of negativerefractive power.

The first lens in the optical imaging system may have a surfaceincluding the most convex point. In detail, the object-side surface ofthe first lens may include the most convex point. The second lens in theoptical imaging system may have substantially a surface including themost concave point. In detail, an image-side surface of the second lensmay include the most concave point.

A focal length of lenses forming the optical imaging system may beselected from within a predetermined range. For example, a focal lengthof the first lens is selected from within a range of 2.2 mm to 2.8 mm, afocal length of the second lens is selected from within a range of −7.0mm to −4.0 mm, a focal length of the third lens is selected from withina range of −21 mm to −10 mm, a focal length of the fourth lens isselected from within a range of −31 mm to −10 mm, and a focal length ofthe sixth lens is selected from within a range of −6.0 mm to −3.0 mm.The ranges are examples, and thus other ranges and combinations ofranges may be apparent after an understanding of the disclosure of thisapplication.

In the optical imaging system, thicknesses of lenses may be different.In detail, among the first to seventh lenses, the first lens may be thethickest, while the second lens or the sixth lens may be the thinnest.Odd-numbered lenses may be substantially thicker than even-numberedlenses disposed adjacently thereto. In an example, the first lens isthicker than the second lens, while the third lens is thicker than thesecond lens and the fourth lens.

Distances between lenses in the optical imaging system may be different.As an example, a distance between the fifth lens and the sixth lens isthe longest, while a distance between the first lens and the second lensis the shortest.

Subsequently, an optical imaging system according to various exampleswill be described. First of all, the optical imaging system according toa first example will be described with reference to FIG. 1. An opticalimaging system 100 includes a first lens 110, a second lens 120, a thirdlens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, and aseventh lens 170.

The first lens 110 has a positive refractive power and opposing convexsurfaces. The second lens 120 has a negative refractive power, a convexobject-side surface, and a concave image-side surface. The third lens130 has a negative refractive power, a convex object-side surface, and aconcave image-side surface. The fourth lens 140 has a negativerefractive power, a concave object-side surface, and a convex image-sidesurface.

The fifth lens 150 has a negative refractive power, a concaveobject-side surface, and a convex image-side surface. The sixth lens 160has a negative refractive power and opposing concave surfaces. Inaddition, the sixth lens 160 includes inflection points formed onopposing surfaces. The seventh lens 170 has a positive refractive powerand opposing convex surfaces. In addition, the seventh lens 170 includesinflection points formed on opposing surfaces.

In the configuration described above, first lens 110 has the highestdegree of positive refractive power, while sixth lens 160 has thehighest degree of negative refractive power. In the example describedabove, an object-side surface of first lens 110 is more convex thansurfaces of other lenses, while the image-side surface of third lens 130is more concave than surfaces of other lenses. In the configurationdescribed above, a paraxial region of first lens 110 is formed to bethicker than paraxial regions of other lenses. Paraxial regions ofeven-numbered lenses 120, 140, and 160 are formed to be thinner thanparaxial regions of odd-numbered lenses 110, 130, 150, and 170. In theexample described above, a distance between fifth lens 150 and sixthlens 160 is longer than that between other lenses. A distance betweenfirst lens 110 and second lens 120 is shorter than that between otherlenses.

Optical imaging system 100 further includes a filter 180, an imagesensor 190, and a stop ST. Filter 180 is interposed between seventh lens170 and image sensor 190, while stop ST is interposed between third lens130 and fourth lens 140.

A refractive index of first lens 110, a refractive index of third lens130, and a refractive index of sixth lens 160 in the optical imagingsystem 100, are lower than or equal to 1.55. In this case, therefractive index of the first lens 110 is substantially the same as thatof the third lens 130. The refractive index of second lens 120 and therefractive index of seventh lens 170, in the optical imaging system 100,are higher than or equal to 1.64.

An effective diameter of a lens in the optical imaging system 100 may begradually reduced in a direction toward the stop ST. For example, aneffective diameter of third lens 130 disposed adjacently to stop ST oran effective diameter of fourth lens 140 are smaller than effectivediameters of lenses adjacent thereto. In a manner different from thecase described above, a lens disposed distantly from stop ST may have arelatively large effective diameter. As an example, the seventh lens 170disposed farthest from stop ST has the largest effective diameter.

An optical imaging system having the configuration described above hasaberration characteristics as illustrated by the graphs in FIG. 2. FIG.3 lists aspherical characteristics of the optical imaging systemaccording to the example. Table 1 lists lens characteristics of theoptical imaging system according to the example.

TABLE 1 First Example EPD = 2.321 f = 6.0350 TL = 5.180 Sur- Refrac-Abbe face Radius of Thickness/ Focal tive Num- No. Curvature DistanceLength Index ber S1 First Lens 1.3800 0.8000 2.440 1.537 56.0 S2−20.9000 0.0800 S3 Second 5.6400 0.1500 −6.040 1.661 20.4 Lens S4 2.33000.2900 S5 Third 2.9400 0.2300 −11.950 1.537 56.0 Lens S6 1.9600 0.1200S7 Stop infinity 0.1400 S8 Fourth −8.0500 0.1500 −12.560 1.636 23.9 LensS9 −10697.340 0.2500 S10 Fifth Lens −12.8900 0.1800 −23.650 1.636 23.9S11 −86.4400 0.9200 S12 Sixth Lens −3.7000 0.1500 −4.990 1.544 56.0 S1310.5300 0.1500 S14 Seventh 15.6700 0.7400 7.510 1.651 21.5 S15 Lens−7.0800 0.1000 S16 Filter infinity 0.1100 1.519 64.2 S17 infinity 0.6200

An optical imaging system according to a second example will bedescribed with reference to FIG. 4. An optical imaging system 200includes a first lens 210, a second lens 220, a third lens 230, a fourthlens 240, a fifth lens 250, a sixth lens 260, and a seventh lens 270.

The first lens 210 has a positive refractive power and opposing convexsurfaces. The second lens 220 has a negative refractive power, a convexobject-side surface, and a concave image-side surface. The third lens230 has a negative refractive power, a convex object-side surface, and aconcave image-side surface. The fourth lens 240 has a negativerefractive power, a concave object-side surface, and a convex image-sidesurface.

The fifth lens 250 has a negative refractive power, a convex object-sidesurface, and a concave image-side surface. The sixth lens 260 has anegative refractive power and opposing concave surfaces. In addition,the sixth lens 260 includes inflection points formed on opposingsurfaces. The seventh lens 270 has a positive refractive power andopposing convex surfaces. In addition, the seventh lens 270 includesinflection points formed on opposing surfaces.

In the configuration described above, first lens 210 has the highestdegree of positive refractive power, while sixth lens 260 has thehighest degree of negative refractive power. In the example describedabove, an object-side surface of first lens 210 is more convex thansurfaces of other lenses, while the image-side surface of second lens220 is more concave than surfaces of other lenses. In the configurationdescribed above, a paraxial region of the first lens 210 is formed to bethicker than paraxial regions of other lenses. Thicknesses of paraxialregions of fourth lens 240 to sixth lens 260 are formed to besubstantially the same. In the example described above, a distancebetween the fifth lens 250 and the sixth lens 260 is longer than thatbetween other lenses. A distance between first lens 210 and second lens220 is shorter than that between other lenses.

The optical imaging system 200 further includes a filter 280, an imagesensor 290, and a stop ST. Filter 280 is interposed between seventh lens270 and image sensor 290, while stop ST is interposed between third lens230 and fourth lens 240.

A refractive index of first lens 210, a refractive index of third lens230, a refractive index of fifth lens 250, and a refractive index ofsixth lens 260, in the optical imaging system 200, are lower than orequal to 1.55. In this case, the refractive index of first lens 210 issubstantially the same as that of third lens 230. The refractive indexof second lens 220 and the refractive index of seventh lens 270, in theoptical imaging system 200, are higher than or equal to 1.64. In opticalimaging system 200, second lens 220 may have substantially the highestrefractive index, while first lens has substantially the lowestrefractive index.

An effective diameter of a lens in the optical imaging system 200 may begradually reduced in a direction toward stop ST. For example, aneffective diameter of fourth lens 240 disposed adjacently to stop ST maybe smaller than effective diameters of lenses adjacent thereto. In amanner different from the case described above, a lens disposeddistantly from stop ST may have a relatively large effective diameter.For example, seventh lens 270 disposed farthest from stop ST has thelargest effective diameter.

An optical imaging system having the configuration described aboverepresents aberration characteristics as illustrated by the graphs inFIG. 5. FIG. 6 lists aspherical characteristics of the optical imagingsystem according to the example. Table 2 lists lens characteristics ofthe optical imaging system according to the example.

TABLE 2 Second Example EPD = 2.321 f = 6.0350 TL = 5.180 Sur- Refrac-Abbe face Radius of Thickness/ Focal tive Num- No. Curvature DistanceLength Index ber S1 First Lens 1.4000 0.7690 2.500 1.537 56.0 S2−27.2300 0.0800 S3 Second 4.8800 0.1520 −5.900 1.661 20.4 Lens S4 1.97000.2250 S5 Third 3.2000 0.2120 −19.960 1.537 56.0 Lens S6 2.4100 0.1580S7 Stop infinity 0.2400 S8 Fourth −8.9200 0.1500 −29.940 1.636 23.9 LensS9 −16.760 0.1000 S10 Fifth Lens 6.4800 0.1500 −30.220 1.544 56.0 S114.6200 1.1280 S12 Sixth Lens −3.5000 0.1500 −4.490 1.544 56.0 S13 8.35000.1710 S14 Seventh 18.8600 0.6650 9.030 1.651 21.5 S15 Lens −8.54000.1000 S16 Filter infinity 0.1100 1.519 64.2 S17 infinity 0.6200

An optical imaging system according to a third example will be describedwith reference to FIG. 7. An optical imaging system 300 includes a firstlens 310, a second lens 320, a third lens 330, a fourth lens 340, afifth lens 350, a sixth lens 360, and a seventh lens 370.

The first lens 310 has a positive refractive power and opposing convexsurfaces. The second lens 320 has a negative refractive power, a convexobject-side surface, and a concave image-side surface. The third lens330 has a negative refractive power, a convex object-side surface, and aconcave image-side surface. The fourth lens 340 has a negativerefractive power, a concave object-side surface, and a convex image-sidesurface.

The fifth lens 350 has a negative refractive power, a convex object-sidesurface, and a concave image-side surface. The sixth lens 360 has anegative refractive power and opposing concave surfaces. In addition,the sixth lens 360 includes inflection points formed on opposingsurfaces. The seventh lens 370 has a positive refractive power andopposing convex surfaces. In addition, the seventh lens 370 includesinflection points formed on opposing surfaces.

In the configuration described above, first lens 310 has the highestdegree of positive refractive power, while sixth lens 360 has thehighest degree of negative refractive power. In the example describedabove, an object-side surface of first lens 310 is more convex thansurfaces of other lenses, while the image-side surface of the secondlens 320 is more concave than surfaces of other lenses. In theconfiguration described above, a paraxial region of first lens 310 isformed to be thicker than paraxial regions of other lenses. In theexample described above, a distance between fifth lens 350 and sixthlens 360 is longer than that between other lenses. A distance betweenthe first lens 310 and the second lens 320 and a distance between thesixth lens 360 and the seventh lens 370 may be shorter than that betweenother lenses.

The optical imaging system 300 further includes a filter 380, an imagesensor 390, and a stop ST. Filter 380 is interposed between seventh lens370 and image sensor 390, while stop ST is interposed between third lens330 and fourth lens 340.

A refractive index of first lens 310, a refractive index of third lens330, a refractive index of fifth lens 350, and a refractive index ofsixth lens 360, in the optical imaging system 300, may be lower than orequal to 1.55. In this case, the refractive index of first lens 310 issubstantially the same as that of third lens 330. The refractive indexof second lens 320 and the refractive index of seventh lens 370, in theoptical imaging system 300, are higher than or equal to 1.64. In theoptical imaging system 300, second lens 320 may have substantially thehighest refractive index, while first lens 310 may have substantiallythe lowest refractive index.

An effective diameter of a lens in optical imaging system 300 may begradually reduced in a direction toward stop ST. For example, aneffective diameter of fourth lens 340 disposed adjacently to stop ST maybe smaller than effective diameters of lenses adjacent thereto. In amanner different from the case described above, a lens disposeddistantly from stop ST may have a relatively large effective diameter.For example, seventh lens 370 disposed farthest from stop ST alternatelyhas the largest effective diameter.

An optical imaging system having the configuration described aboverepresents aberration characteristics as illustrated in the graphs inFIG. 8. FIG. 9 lists aspherical characteristics of the optical imagingsystem according to the example. Table 3 lists lens characteristics ofthe optical imaging system according to the example.

TABLE 3 Third Example EPD = 2.321 f = 6.0340 TL = 5.179 Sur- Refrac-Abbe face Radius of Thickness/ Focal tive Num- No. Curvature DistanceLength Index ber S1 First Lens 1.4000 0.7610 2.510 1.537 56.0 S2−28.1900 0.0800 S3 Second 4.8500 0.1500 −5.150 1.661 20.4 Lens S4 1.99000.2500 S5 Third 3.1400 0.2310 −16.470 1.537 56.0 Lens S6 2.2600 0.1280S7 Stop infinity 0.1210 S8 Fourth −10.3700 0.1610 −26.390 1.636 23.9Lens S9 −26.980 0.1000 S10 Fifth Lens 5.3800 0.1500 −60.070 1.544 56.0S11 4.5800 1.2560 S12 Sixth Lens −3.4600 0.1500 −4.670 1.544 56.0 S139.9000 0.1770 S14 Seventh 15.9300 0.6300 10.830 1.651 21.5 Lens S15−12.6700 0.1000 S16 Filter infinity 0.1100 1.519 64.2 S17 infinity0.6242

An optical imaging system according to a fourth example will bedescribed with reference to FIG. 10. An optical imaging system 400includes a first lens 410, a second lens 420, a third lens 430, a fourthlens 440, a fifth lens 450, a sixth lens 460, and a seventh lens 470.

The first lens 410 has a positive refractive power and opposing convexsurfaces. The second lens 420 has a negative refractive power, a convexobject-side surface, and a concave image-side surface. The third lens430 has a negative refractive power, a convex object-side surface, and aconcave image-side surface. The fourth lens 440 has a negativerefractive power, a concave object-side surface, and a convex image-sidesurface.

The fifth lens 450 has a positive refractive power, a convex object-sidesurface, and a concave image-side surface. The sixth lens 460 has anegative refractive power and opposing concave surfaces. In addition,the sixth lens 460 includes inflection points formed on opposingsurfaces. The seventh lens 470 has a negative refractive power andopposing convex surfaces. In addition, the seventh lens 470 includesinflection points formed on opposing surfaces.

In the configuration described above, first lens 410 has the highestdegree of positive refractive power, while sixth lens 460 has thehighest degree of negative refractive power. In the example describedabove, an object-side surface of first lens 410 is more convex thansurfaces of other lenses, while the image-side surface of second lens420 is more concave than surfaces of other lenses. In the configurationdescribed above, a paraxial region of first lens 410 is formed to bethicker than paraxial regions of other lenses. A paraxial region offifth lens 450 is formed to be thinner than paraxial regions of otherlenses. In the example described above, a distance between fifth lens450 and sixth lens 460 is longer than that between other lenses. Adistance between first lens 410 and second lens 420 is shorter than thatbetween other lenses.

The optical imaging system 400 further includes a filter 480, an imagesensor 490, and a stop ST. Filter 480 is interposed between seventh lens470 and image sensor 490, while stop ST is interposed between third lens430 and fourth lens 440.

A refractive index of first lens 410, a refractive index of third lens430, a refractive index of fifth lens 450, and a refractive index ofsixth lens 460, in optical imaging system 400, may be lower than orequal to 1.55. The refractive index of second lens 420 and therefractive index of seventh lens 470, in the optical imaging system 400,are higher than or equal to 1.65. In the optical imaging system 400,second lens 420 may have substantially the highest refractive index,while first lens 410 may have substantially the lowest refractive index.The refractive index of fourth lens 440, in the optical imaging system400, is higher than or equal to 1.6.

An effective diameter of a lens in the optical imaging system 400 may begradually reduced in a direction toward stop ST. For example, aneffective diameter of third lens 430 disposed adjacently to stop ST issmaller than effective diameters of lenses adjacent thereto. In a mannerdifferent from the case described above, a lens disposed distantly fromstop ST may have a relatively large effective diameter. For example,seventh lens 470 disposed farthest from stop ST has the largesteffective diameter.

An optical imaging system having the configuration described aboverepresents aberration characteristics as illustrated by the graphs inFIG. 11. FIG. 12 lists aspherical characteristics of the optical imagingsystem according to the example. Table 4 lists lens characteristics ofthe optical imaging system according to the example.

TABLE 4 Fourth Example EPD = 2.327 f = 6.0489 TL = 5.232 Sur- Refrac-Abbe face Radius of Thickness/ Focal tive Num- No. Curvature DistanceLength Index ber S1 First Lens 1.4100 0.7720 2.530 1.537 56.0 S2−31.6900 0.0800 S3 Second 4.8700 0.2000 −5.050 1.661 20.4 Lens S4 1.96000.2610 S5 Third 3.2900 0.2320 −15.620 1.544 56.0 Lens S6 2.3100 0.1180S7 Stop infinity 0.1350 S8 Fourth −8.4300 0.2000 −18.980 1.636 23.9 LensS9 −27.700 0.1000 S10 Fifth Lens 5.0500 0.1700 420.180 1.544 56.0 S115.1100 1.1670 S12 Sixth −3.4600 0.2000 −4.950 1.544 56.0 Lens S1312.7300 0.1270 S14 Seventh 733.4600 0.6290 −10.95 1.651 21.5 Lens S15−7.2700 0.1000 S16 Filter infinity 0.1100 1.519 64.2 S17 infinity 0.6313

Table 5 lists values of Conditional Equations of the optical imagingsystem according to first to fourth examples.

TABLE 5 Conditional First Second Third Fourth Equation Example ExampleExample Example TL/f 0.8583 0.8583 0.8583 0.8650 f/(Img HT) 2.321 2.3212.414 2.240 Nd5 1.636 1.544 1.544 1.544 Nd7 1.651 1.651 1.651 1.651 f5/f−3.919 −5.007 −9.955 69.46 f/EPD 2.60 2.60 2.60 2.60

Hereinafter, a portable terminal including an optical imaging systemmounted therein, according to an example, will be described withreference to FIGS. 13 and 14. A portable terminal 10 includes aplurality of camera modules 20 and 30. A first camera module 20 includesa first optical imaging system 101 configured to capture an image of asubject at a short distance. A second camera module 30 includes secondoptical imaging systems 100, 200, 300, and 400 formed to capture animage of a distant subject.

The first optical imaging system 101 includes a plurality of lenses. Forexample, the first optical imaging system 101 may include four or morelenses. The first optical imaging system 101 is configured to captureimages of objects at short distance. In detail, first optical imagingsystem 101 may have a relatively wide angle of view of 50° or above,while a ratio (TL/f) may be higher than or equal to 1.0.

The second optical imaging systems 100, 200, 300, and 400 include aplurality of lenses. For example, second optical imaging systems 100,200, 300, and 400 may include seven lenses. The second optical imagingsystems 100, 200, 300, and 400 may be provided as one optical imagingsystem among optical imaging systems according to the first to fourthexamples described above. The second optical imaging systems 100, 200,300, and 400 may be configured to capture an image of a distant object.In detail, second optical imaging systems 100, 200, 300, and 400 mayhave a half angle of view of 20° or above, while a ratio (TL/f) may bebelow 1.0.

First optical imaging system 101 and second optical imaging systems 100,200, 300, and 400 may have substantially the same size. In detail, anoverall length L1 of first optical imaging system 101 is substantiallythe same as an overall length L2 of second optical imaging systems 100,200, 300, and 400. Alternatively, a ratio (L1/L2) of the overall lengthL1 of first optical imaging system 101 to overall length L2 of thesecond optical imaging systems 100, 200, 300, and 400 may be 0.8 to 1.0.Alternatively, a ratio (L2/h) of the overall length L2 of the secondoptical imaging systems 100, 200, 300, and 400 to a thickness h of theportable terminal 10 may be lower than or equal to 0.8.

As set forth above, according to examples, an optical imaging systemcapable of capturing images of distant objects and being mounted in asmall terminal may be provided. While this disclosure includes specificexamples, it will be apparent after an understanding of the disclosureof this application that various changes in form and details may be madein these examples without departing from the spirit and scope of theclaims and their equivalents. The examples described herein are to beconsidered in a descriptive sense only, and not for purposes oflimitation. Descriptions of features or aspects in each example are tobe considered as being applicable to similar features or aspects inother examples. Suitable results may be achieved if the describedtechniques are performed in a different order, and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner, and/or replaced or supplemented by other components ortheir equivalents. Therefore, the scope of the disclosure is defined notby the detailed description, but by the claims and their equivalents,and all variations within the scope of the claims and their equivalentsare to be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system, comprising: a firstlens comprising a positive refractive power; a second lens comprising anegative refractive power; a third lens comprising a negative refractivepower; a fourth lens comprising a negative refractive power; a fifthlens; a sixth lens; and a seventh lens, wherein the first lens to theseventh lens are sequentially disposed from an object side to an imagingplane, wherein the optical imaging system satisfies the followingexpression: Nd2<1.67 where Nd2 represents a refractive index of thesecond lens.
 2. The optical imaging system of claim 1, wherein theoptical imaging system satisfies the following expression: 0.7<TL/f<1.0where TL represents a distance from an object-side surface of the firstlens to an imaging plane, and f represents an overall focal length ofthe optical imaging system.
 3. The optical imaging system of claim 1,wherein the optical imaging system satisfies the following expression:0.1<f/(Img HT)<2.5 where f represents the overall focal length of theoptical imaging system, and IMG HT represents a half diagonal length ofthe imaging plane.
 4. The optical imaging system of claim 1, wherein theoptical imaging system satisfies the following expression: 1.5<Nd5<1.7where Nd5 represents a refractive index of the fifth lens.
 5. Theoptical imaging system of claim 1, wherein the optical imaging systemsatisfies the following expression: 1.6<Nd7 where Nd7 represents arefractive index of the seventh lens.
 6. The optical imaging system ofclaim 1, wherein the optical imaging system satisfies the followingexpression: -70<f5/f<70 where f represents the overall focal length ofthe optical imaging system, and f5 represents a focal length of thefifth lens.
 7. The optical imaging system of claim 1, wherein theoptical imaging system satisfies the following expression: 2.4<f/EPD<2.8where f represents the overall focal length of the optical imagingsystem, and EPD represents a diameter of an entrance pupil.
 8. Anoptical imaging system, comprising: a first lens comprising a positiverefractive power; a second lens comprising a negative refractive power;a third lens comprising a negative refractive power; a fourth lenscomprising a negative refractive power; a fifth lens; a sixth lenscomprising a negative refractive power; and a seventh lens comprises aconvex object-side surface along an optical axis and a convex image-sidesurface along the optical axis, wherein the first lens to the seventhlens are sequentially disposed from an object side to an imaging plane.9. The optical imaging system of claim 8, wherein each of the first toseventh lenses have an aspheric surface.
 10. The optical imaging systemof claim 8, wherein the first lens comprises a convex object-sidesurface having a most convex point of the optical imaging system andwherein the second lens has a concave image-side surface having a mostconcave point of the optical imaging system.